Magnetic amplifiers and apparatus

ABSTRACT

A magnetic amplifier is proposed especially for use in traction and/or braking control systems for railways in which control is in response to an analog current flowing in a wire running down the train. The magnetic amplifier is provided with a shorted turn which has the effect of making the amplifier largely independent of d.c. control source impedance variations thereby avoiding requirements for recalibration when the cars of a train are changed for example.

United States Patent 1 91 1111 3,724,392 Maskery [451 Apr. 3, 1973 1541 MAGNETIC AMPLIFIERS AND 3,085,208 4/1963 Darling ..323/89 R APPARATUS 3,088,039 4/1963 Wanlass ..323/89 0 2,412,864 12 1946 B t l. .323 89 M [75] inventor: Arthur Maskery, London, England owman e a l [7 3] Assignee: Westinghouse Brake and Signal Primary Examiner-Robert G. Sheridan Co p y, Limited, London, g- Assistant Examiner-George H. Libman land Attorney-Larson, Taylor & Hinds [22] Filed: Oct. 26, 1970 [21] Appl. No.: 83,731 57 ABSTRACT A magnetic amplifier is proposed especially for use in [30] Foreign Appuntion Priority Data traction and/or braking control systems for railways in Nov. 5, 1969 Great Britain ..54,l42/69 which co is in response to an analog current flowing in a wire running down the train. The magnetic [52] [1.5. CI ..l05/61, 180/105 E, 303/20, amplifier is provided with a shorted turn which has the 323/39 330/3 effect of making the amplifier largely independent of [5 Int. "B618 d c control source impedance variations thereby [58] Field of search-"323mg 89 89 M; 330/8; avoiding requirements for recalibration when the cars 105/61; 180/105 E; 303/20 of a train are changed for example.

[56] References Cited 3 Claims, 5 Drawing Figures UNITED STATES PATENTS 2,677,800 5/1954 Phillips ..330/8 BRAKE BRAKE 1 1 BLENDlNG BOX l g i BB1 TRACTION BBN 4 MAGNETIC AMPLIFIER TRACTION c MAI MAGNETIC *CONTROLLER TRAIN WI RE BLENDING BOX \MAGNETIC AMPLIFIER I I TRACTION :-MAN l BRAKE MAI 1 ,BLENDING BOX BRAKE BBI' CONTROLLER PATENTEU N O s o 2 S m F b C. WU f A RM 0 R B w B D a m T E m l- 2 ww A Q A 2 N S N s m i w m l fi nu qq qaqqb m N 1 f -w w n C 0 55513 .5156 H MAGNETIC AMPLIFIERS AND APPARATUS The present invention relates to magnetic amplifiers and relates especially but not exclusively to a magnetic amplifier for connection with control windings in series with the control windings of further magnetic amplifiers to operate separate sets of control apparatus from a common d.c. control signal.

In railway vehicle braking systems it has been proposed to control braking of a train by transmitting via a train wire a control current along the train, each car of the train having braking and/or traction apparatus controlled by the output derived from a magnetic amplifier the control winding of which carries the current in the train wire. All such magnetic amplifiers are connected by being interposed in the train wire to be in series to enable each to be responsive to the same control current. The use of current control is preferable to voltage control since the number of magnetic amplifiers employed, and therefore the number of cars in the train can thereby be arranged to be of no consequence, there being no question of voltage sharing in-. fiuencing the signal. Again, by employing series connection of the control windings of the magnetic amplifiers in the control wire, questions of current sharing between them do not arise. The signals derived from the magnetic amplifiers are utilized inter alia, to control suitable respective equipments to effect braking and/or traction in accordance with the control current in the train wire. Typically, the control current may be arranged to command vehicle coasting at a half ampere, controllable degrees of braking in the region of one half to zero amperes and controllable degrees of traction in the region of one half to l ampere of train wire current.

In such a system, where the current is supplied to the train wire from a so-called constant current source, it is found that the magnetic amplifiers may exhibit a nonlinear region of their response characteristic. for low values of control current and this is disadvantageous and does not meet customers specifications for certain equipments. Moreover, the impedance of the circuit feeding any given magnetic amplifiers tends to influence the characteristic. The source impedance can never be regarded as constant owing to variability in practice of the number of magnetic amplifiers, the control windings of which are connected in series, when the number of cars on a train is changed. It is a substantial disadvantage moreover if equipments have to be readjusted to present a desired value of input circuit impedance every time that there is a change of cars on a train. Obviously, it may be said that in order to obtain a given ampere-tums value for the control windings of a magnetic amplifier without introducing a substantial impedance, a high cross-sectional area of the windings conductors may be envisaged but this is uneconomic and impracticable when it is remembered that usually the magnetic amplifier cores, in order to have suitable magnetization characteristics are arranged as toroids and can accommodate only a limited amount of copper for windings.

According to the present invention there is provided a magnetic amplifier having a.c. supply windings and d.c. control windings and an additional virtually shortcircuited winding operable to render the control characteristic of the magnetic amplifier largely independent of impedance changes in series with the d.c. control windings.

The invention further provides such a magnetic am plifier connected to receive at the d.c. control windings an electrical command analogue signal indicative of a desired rate of change of speed, andhaying the a.c. supply windings connected in a circuit current in which in operation is applied to means for controlling the magnitude of a force acting to effect a change of speed of a vehicle.

In order that the invention may be more clearly understood and readily carried into effect the invention will be further described by way of example with reference to the accompanying drawing in which:

FIG. 1 illustrates in diagrammatical form an outline train control system employing magnetic amplifiers.

FIG. 2 illustrates some magnetic amplifier characteristics to be referred to,

FIG. 3 illustrates a magnetic amplifier in diagrammatical manner,

FIG. 4 illustrates a magnetic amplifier and FIG. 5 illustrates in block form one apparatus employing such a magnetic amplifier.

Referring to the drawing, FIG. 1 illustrates diagrammatically two of a number of magnetic amplifiers MAl to MAN connected with their d.c. control windings in series in a train wire which derives its control signal via a drivers controller C. The magnetic amplifiers MAI to MAN are each connected to signal processing units which may be called blending boxes and are indicated by references BB1 to BBN. These units are operable to produce output E.P. (electro-pneumatic) braking or traction control signals dependent not only upon the d.c. control signal applied to the train wire but also upon the rail vehicle loadings and in the case of braking the degree of dynamic braking available. Such a system will be discussed in somewhat greater detail hereafter with reference to FIG. 4.

For proposed control systems, definite limits have been specified for the input impedances of the magnetic amplifiers and forthe reasons indicated, it is not always practicable to design magnetic amplifiers with such low input impedances as have been specified. Additionally, it will be appreciated from the above that even if the input impedances are kept to a low value, impedances far in excess of the input impedances of the magnetic amplifiers may inadvertently be introduced into the train wire circuit by, for example, inter-car couplers which may be employed for connecting the wire of one car to the wire of the next car to complete the control circuit. Such impedances are cummulat ive and present themselves as a source impedance to any given magnetic amplifier in the system. This can not only adversely affect the overall operating characteristic thereof but more particularly, such an impedance can also introduce a non-linear region at the lower end of the characteristic.

The above effect is illustrated in FIG. 2 which shows in a broken line, a typical magnetic amplifier characteristic with input d.c. milliamps plotted against output rectified milliamps. This clearly demonstrates the non-' linear part of the characteristic for lower values of control current, the zero-shift representing the core material magnetizing current.

A typical construction of a magnetic amplifier consists of a pair of toroidal cores, preferably of high permeability steel, each one with output winding turns the windings on each being connected in series and a v control winding wound commonly about the two cores. The output is derived in the application presently being discussed by rectification of the input alternating current signal applied to a load via the above series windings.

It will be seen that peculiarly advantageous effects are to be obtained by. adding to such a magnetic amplifier' a substantially short-circuited winding consisting of one or more than one turn, about the two cores. This winding presents an exceedingly low impedance to that core which at a specified time is operating in transformer manner whilst the other core is saturated. When the present invention is applied, a typical operating characteristic is as shown by the solid line in FIG. 2.

Reference may now be made to FIG. 3 of the drawings which shows a magnetic amplifier in typical diagrammatical form. The common d.c. control windingv of the magnetic amplifier is shown as two like windings NCl and NC2 on respective magnetizable cores these cores having respective equal series-connected a.c. windings NAl and NA2. The senses of the windings NA] and NA2 are mutually opposite as compared to those of NCl and NC2, the relative senses of the windings being indicated by dots on the drawing. A bridge'rectifier BR is connected in series between the a.c. supply terminals of the magnetic amplifier and the windings NAl and NA2. The d.c. output of the bridge rectifier is connected to a load represented by the blocklL.Addi'tionally, a pair of windings NS] and NS2 are provided connected in series through a short circuit. Typically, windings NS1 and NS2 in practice comprise a single turn embracing both cores.

The magnetic amplifier is designed such that each of the cores SCI and SC2 is capable of supporting the full a.c. voltage. In normal operation, one core is saturated at or near the beginning of a half cycle of the a.c. supply source supplying the transductor. In general, due to the well known results of ampere-turns equality in the windings of the unsaturated core, there is a linear relationship between the mean rectified output current and the mean d.c. control current. However, where the magnetic amplifier and its circuit characteristics are such that saturation of one of the cores occurs somewhat after the beginning of a half cycle of the a.c. source, this gives rise to a state of affairs in which the above ampereturns relationship only commences to be applicable at such a later instant. This gives rise in turn to a non-linearity between output and control current over values of control current.

Ignoring for the present the shorted windings NS] and N82, the d.c. control current source may be considered to be a constant current high impedance source producing a control current of such a low value that saturation of one of the cores, say core SCl, occurs appreciably after the beginning of a respective a.c. source voltage half cycle. Up to such saturation, in the half cycle, the a.c. source voltage is shared between windings NA! and NA2 and the load L via the bridge rectifier BR. The other windings NCl and NC2 are mutually decoupledwith respect to the a.c. side of the circuit and also only magnetizing current flows in NAl, NA2 and L. When the core SCl saturates, the impedance presented by NAl falls to substantially zero value to transfer the whole of the supply source voltage across the winding NA2 and the load L in series. At this point,

due to the transformer effect over core SC2 and ampere-turns equality in windings NA2 and NC2, the current in winding NA2 now rises to a value dependent upon the control current in NC2.

Consider the situation in which the control current is increased to advance the point in the half cycle at which saturation occurs it will be observed that not only is the period of only magnetizing current reduced but also the value of current which now flows for a longer period following saturation of the core SCI is increased to maintain the ampere-turns equality'in NA2 and NC2. Thus there is an approximately square law relationship between control current and the output current over the part of the characteristic which is being considered. This gives rise to the above mentioned non-linearity which occurs at the lower end of the control characteristic typified by the practical curve shown dotted in FIG. 2 referred to above.

If the control circuit impedance is assumed to be low, the non-linearity is substantially reduced by virtue of the fact that the output current which flows following a point of saturation of one core of the transductor is determined by the impedances in the control circuit and tends always to rise to an approximately constant value for all points at which saturation occurs in a of almost zero value due to the virtual short circuit across winding NS2.

Therefore the value to which current increases from magnetizing current level, on occurrence of saturation of the core SCI, is determined by the supply voltage and the impedance presented by the load L. This current value does not therefore substantially change over the range of points at which saturation can occur due to variation of control current. The mean value of current in L is therefore approximately linearly related to control current over this range. 7

In the event of a reduction (say) of the impedance L, the value of peak current obtained in the load L following saturation of one core (say SCI) is now larger but this is offset by a resultant retardation of the instant at which core saturation occurs in successive half cycles. This is brought about mainly by the increase of the remanent flux set into the unsaturated core in one half cycle and which therefore effects greater voltage-time extraction before saturation of the core in the opposite direction in the next half cycle. Hence, a range of values of load impedance L may be accepted without materially affecting the value of the mean output current produced by a given control current.

Moreover, reference to FIG. 2 indicates the discrepancy between the dotted and solid line characteristics,

This discrepancy represents the range of variation of the control characteristic, for varying values of input circuit impedance, of a magnetic amplifier which is not provided with a winding such as represented by NS1 and NS2 in FIG. 3. The provision of such a winding removes the possibility of such discrepancies occurring and presents substantial advantages in braking control systems utilizing such magnetic amplifiers.

FIG. 4 illustrates in diagrammatical form a sectional view of a magnetic amplifier embodying the present invention. The respective windings and toroidal core of the magnetic amplifier have references corresponding to those referred to above with reference to FIG. 3 and the drawing will therefore be largely self explanatory. Typically however, the a.c. windings NAl and NA2 each consist of 300 turns, the controlling d.c. windings are embraced in a composite winding around both the toroids and typically consist of turns. Again, the shorted windings NS1 and NS2 are provided by a single turn embracing both cores.

A typical apparatus employing a magnetic amplifier as described above is illustrated in block form in FIG. 5 which enlarges upon the contents of a block such as BB1 of FIG. 1. The apparatus is for the purposes of braking and traction control acting in response to the magnitude of an applied d.c. current analogue control signal and the apparatus is suitable for controlling the monitored and brake axles of a train having a number of interconnected cars. A d.c. command analogue signal is derived from a drivers control unit which forms no part of the present apparatus as such the signal being fed to each of the cars in series over a pair of conductors passing the full length of the train and having magnetic amplifiers control windings inserted for deriving control at required points. It is preferable to employ a current analogue signal as mentioned above for the reason that it is possible to provide a constant current supply for the analogue signal whereas if a voltage signal were to be used it would be necessary to compensate for example, for variation of overall voltage drop which occurs with changes of the number of couplings and also to take account of voltage sharing effects.

The present system is arranged not only to control the electro-pneumatic braking facilities of the train and the track facilities provided thereon but also control dynamic braking. A deficiency in the dynamic braking under such control is made up for by electro-pneumatic braking.

It is also desirable in the case of electric traction to control the tractive effort applied to any given car by the motors on the respective bogeys of the car and also to control the braking effective on these cars in accordance with the loading of the bogeys. Accordingly, for each end of a car, load weighing equipment is assumed to be provided and this may for example take the form of suitable means which provides a fluid pressure dependent upon the vehicle loading to a pressure transducer which modifies the accelerating force or the degree of braking individually for the individual bogeys of cars in the train. Thus, whilst a particular current analogue signal is applied from the drivers control equipment to all of the cars on the train, the equipment associated with each bogey of each car modifies the response of the braking apparatus or tractice apparatus in accordance with the loading experienced thereat.

It is a special outcome of the particular equipment i1- lustrated in block form in FIG. 5 that in the unlikely event of failure of the load-weighing equipment on a caror of electronic circuits associated therewith, the

electro-pneumatic braking remains unaffected. This is because the command analogue signal before application to the amplifier which includes the pressure transducer, is applied right around the whole equipment to the summing means to provide at least braking effort up to a said tearway level.

Referring to the block illustration of FIG. 5 the terminals 1 are connected to receive direct current from a magnetic amplifier as discussed above in connection with FIGS. 3 and 4, such an amplifier is fed with 48 volts at 1,000 cycles per second the d.c. output being derived via a rectifier and being connected to a jerk control circuit represented by the block 3. This jerk control unit is provided for ensuring that normally the actual command analogue signal to which the apparatus is responsive cannotchange at more than a predetermined acceptable rate regardless of rate of change of the signal applied to the terminals 1. This is desirable for the two-fold reasons that firstly, the braking must never be allowed to be so excessive as to cause substantial passenger discomfort and secondly, the currents supplied to traction motors are required to be limited to not command the motors to provide more than a predetermined degree of acceleration.

The output of the jerk control unit 3 is also a d.c. analogue signal and in the present example is assumed to be a voltage signal which can vary between 0 and 10 volts. The range 0 to approximately 5 volts corresponds to the braking range of control and the range from approximately 5 to 10 volts corresponds to the range of traction control. Maximum traction force is attained at a value of the command analogue signal of 10 volts and maximum braking is attained at a value of the command analogue signal of approximately zero colts. Typically, the values of input control currents in the train wires giving rise to this full range of 0 to 10 volts is a range of current from 0 to 1 amp.

The command analogue voltage signal is applied to a so-called ring modulator 4 to a second input 5 of which there is applied a 5 volt reference signal the purpose of which will be appreciated hereafter. The ring modulator also receives a basic carrier frequency of 2.5 KHz from a multi-vibrator oscillator represented by the lock 6. The variable signal output of the modulator consists of an a.c. magnitude of which is dependent upon the degree of braking or acceleration called for by the command signal and the phase of which is dependent upon whether the signal represents braking or acceleration. This signal is applied to an amplifier 7 to which a load signal is applied at 7a such that the amplifier produces a weight dependent output signal and this weight dependent output signal is applied to an adding circuit represented by the block 8 to which the output of the ring modulator 4 is additionally applied. The combination of the amplifier 7 and the adding circuit 8 may be regarded as a multiplication circuit. The signal applied from the output of the modulator 4 to the adding circuit 8 can be regarded as a control signal for purely tare weight control on the bogey in question and the amplifier output may be regarded as the extent to which this signal requires to be supplemented for added loading on the vehicle. The output of the adding circuit 8 is therefore an a.c. signal proportional to the required degree of braking for the required degree of acceleration for the portion of the train under consideration and this is therefore termed a load weighted signal. The phase of the signal is the parameter thereof detection of which determines whether the signal is a braking control signal or an acceleration control signal and this is determined by a phase sensitive rectifier 9 which has an output applied to it from the oscillator 6 and which determines whether the output should be on the line 10 for feeding to the dynamic brake control apparatus or to the line 11 for feeding to the traction control apparatus of the particular bogey of the car in question.

A summing circuit is represented by the block 12 and the output of 12 controls the electro-pneumatic braking equipment of the particular bogey on the car in question. The summing circuit 12 receives a signal on the line 13 being a d.c. signal proportional to the command analogue signal and a signal on the line 14 which is a rectified signal proportional to the load responsive signal received from the amplifier 7. A further signal is applied to the input line 15 to circuit 12 and is derived from the dynamic braking portion of the control equipment. This signal is a d.c. signal indicative of the degree of dynamic braking being produced at a material time. A further signal which comprises a fixed bias is applied to the input line 16 of circuit 12 and this provides a basic restricted brake application via the electro-pneumatic brakes and is of such a value as to provide braking merely to take up slack and the like in the brake rigging, in the mechanical parts of the braking equipment before the brakes are actually effective. The summing circuit 12 is therefore arranged to be operative to-blend the electro-pneumatic braking with the dynamic braking to provide the desired degree of braking as determined in accordance with the sum of the signals appearing on lines 13 and 14.

From the foregoing it will be observed that in the event of any of the portions of the circuit consisting of blocks 7, 8 or 9 sustaining a failure, the circuit 12 can continue to receive a control signal in the form of the signal on the line 13 such that the electro-pneumatic braking can be effective to produce braking at least to a tare weight value.

The above description of the apparatus with reference to FIG. 5 is not burdened with technical detail of the contents of the various blocks but a fuller description of the circuit arrangements in these blocks may be had with reference to US. Pat. No. 3,547,499. In that patent a jerk control unit is described as including an input transductor and rectifier which is limited to a unidirectional control. It will be understood however that in the presently proposed system, the magnetic amplifier of FIG. 5 which is controllable with either polarity of current replaces the above input transductor and the various windings upon it.

It will be appreciated that by employing a magnetic amplifier as described earlier, changes in the input circuit impedance associated with the train wire and the series connected magnetic amplifier control windings,

by decreasing the number of cars in a particular train in an application to train control as outlined above may i have negligible effect on the control characteristic of the various equipments and the advantages of such magnetic amplifiers and systems employing them is immediately apparent. 1

Having thus described our invention what we claim 1. A control apparatus for a vehicle comprising a magnetic amplifier comprising d.c. control windings connected to receive an electrical command analog signal indicative of a desired rate of change of speed, a.c. supply windings connected in a circuit the current in which is, in operation, applied to means for controlling the magnitude of a force acting to effect a change in speed of the vehicle, and an additional virtually short-circuited winding for rendering the control characteristic of the magnetic amplifier largely independent of impedance changes in series with the d.c. control windings.

2. In a control system for a vehicle including means for generating an electrical command analog signal indicative of a desired rate of change of speed and means for controlling the magnitude of a force acting to effect a change of speed of the vehicle, the improvement comprising a magnetic amplifier comprising d.c. control windings connected to receive the electrical command analog signal indicative of a desired rate of change of speed, a.c. supply windings connected in a circuit the current in which is, in operation, applied to the means for controlling the magnitude of a force acting to effect a change of speed of the vehicle, and an additional virtually short-circuited winding for rendering the control characteristic of the magnetic amplifier largely independent of impedance changes in series with the d.c. control windings. I

3. In a control system for a vehicle including means for producing an electrical command analog signal indicative of a desired deceleration and braking control means for commanding dynamic braking, a magnetic amplifier comprising d.c. control windings connected to receive the electrical command analog signal indicative of a desired deceleration, a.c. supply windings connected in a circuit the current in which is, in operation, applied to said dynamic control means to command dynamic braking, and an additional virtually short-circuited winding for rendering the control characteristic of the magnetic amplifier largely independent of impedance changes in series with the d.c. control windings, said braking control means being further responsive to an electrical signal indicative of the degree of dynamic braking produced so as to produce an output control signal for controlling additional braking means in order to compensate for any deficiency in the dynamic braking commanded by the command analog signal. 

1. A control apparatus for a vehicle comprising a magnetic amplifier comprising d.c. control windings connected to receive an electrical command analog signal indicative of a desired rate of change of speed, a.c. supply windings connected in a circuit the current in which is, in operation, applied to means for controlling the magnitude of a force acting to effect a change in speed of the vehicle, and an additional virtually short-circuited winding for rendering the control characteristic of the magnetic amplifier largely independent of impedance changes in series with the d.c. control windings.
 2. In a control system for a vehicle including means for generating an electrical command analog signal indicative of a desired rate of change of speed and means for controlling the magnitude of a force acting to effect a change of speed of the vehicle, the improvement comprising a magnetic amplifier comprising d.c. control windings connected to receive the electrical command analog signal indicative of a desired rate of change of speed, a.c. supply windings connected in a circuit the current in which is, in operation, applied to the means for controlling the magnitude of a force acting to effect a change of speed of the vehicle, and an additional virtually short-circuited winding for rendering the control characteristic of the magnetic amplifier largely independent of impedance changes in series with the d.c. control windings.
 3. In a control system for a vehicle including means for producing an electrical command analog signal indicative of a desired deceleration and braking control means for commanding dynamic braking, a magnetic amplifier comprising d.c. control windings connected to receive the electrical command analog signal indicative of a desired deceleration, a.c. supply windings connected in a circuit the current in which is, in operation, applied to said dynamic control means to command dynamic braking, and an additional virtually short-circuited winding for rendering the control characteristic of the magnetic amplifier largely independent of impedance changes in series with the d.c. control windings, said braking control means being further responsive to an electrical signal indicative of the degree of dynamic braking produced so as to produce an output control signal for controlling additional braking means in order to compensate for any deficiency in the dynamic braking commanded by the command analog signal. 